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097-55501-01 Revision M – January 2009
TimeHub 5500 User’s Guide
81
Chapter 2 Engineering Ordering Information
NTP Server Card
Keyword NTPSLOT=ACT manually sets the selected NPT card to be the active
card.
Keyword NTPSLOT=ACTA manually sets Port A of one selected NTP card to be
the active port, but does not change the active/standby status of the card. In
other words, if the card is an active card, Port A becomes the active port; if the
card is in standby mode, Port A becomes the standby active port. When the
system does a card switchover from the active card, this will become the active
port.
Keyword NTPSLOT=ACTB manually sets Port B of one selected NTP card to be
the active port, but does not change the active/standby status of the card.
Keyword NTPPAIR=ACTA manually sets Port A on both active and standby
cards to be the active port, but does not change the active/standby status of
either card. In other words, Port A on the active card will be the active port, and
Port A on the standby card will be the standby active port.
Keyword NTPPAIR=ACTB manually sets Port B on both active and standby
cards to be the active port, but does not change the active/standby status of
either card.
NTP Traffic Load Limit
The TimeHub NTP Server card implements traffic control to prevent the complete
loading down of the NTP card processor from excessive traffic on any NTP port.
When traffic control is not activated, a NTP Server card will accept packets from
both NTP ports on a first-come-first-served basis. When in any one-second interval
the combined traffic loading from port A and port B has reached the packet
processing limit of the card, all subsequent packets will be dropped for the rest of
this one-second interval. The current packet processing limits are 1000
authenticated packets or 1500 unauthenticated packets per one-second interval.
This capacity assumes that the incoming packets are distributed evenly in time.
Actually the hardware that limits the input packets does not know whether a packet
is NTP or whether it is authenticated. The hardware uses packet length to decide
whether a packet may be an authenticated NTP packet or unauthenticated NTP
packet. The threshold NTP packet length it uses to make this decision is 92 bytes
(this is the Ethernet frame length of an unauthenticated NTP packet). If a NTP
packet length has 92 or fewer bytes, it is classified as an unauthenticated NTP
packet. If the length is more than 92 bytes, it is considered an authenticated NTP
packet. A counter is used to keep track how many packets have been accepted
within a one-second interval. When a short packet (“unauthenticated”) is accepted,
the counter is incremented by 2. When a long packet (“authenticated”) is accepted,
the counter is incremented by 3. The counter threshold is 3000 within a one-second
interval. When the count reaches 3000, no more packets are accepted until the
counter is reset for the next 1 second interval. This counter is reset once a second.
Содержание TimeHub 5500
Страница 1: ...TimeHub 5500 User s Guide Revision M January 2009 Part Number 097 55501 01 ...
Страница 12: ...List of Figures 12 TimeHub 5500 User s Guide 097 55501 01 Revision M October 2008 ...
Страница 14: ...List of Tables 14 TimeHub 5500 User s Guide 097 55501 01 Revision M January 2009 ...
Страница 46: ...46 TimeHub 5500 User s Guide 097 55501 01 Revision M January 2009 Chapter 1 Description TimeScan THC Software ...
Страница 280: ...280 TimeHub 5500 User s Guide 097 55501 01 Revision M January 2009 Chapter 6 Specifications Factory Default Values ...